Limit number of shown environments for Merge Requests

- For target project show only environments for target branch or with tags
- For source project show only environments for source branch

app/models/merge_request.rb

@@ -670,9 +670,12 @@ class MergeRequest < ActiveRecord::Base
   def environments
     return [] unless diff_head_commit
 
-    target_project.environments.select do |environment|
-      environment.includes_commit?(diff_head_commit)
-    end
+    environments = source_project.environments_for(
+      source_branch, diff_head_commit)
+    environments <<= target_project.environments_for(
+      source_branch, diff_head_commit, with_tags: true)
+
+    environments
   end
 
   def state_human_name

app/models/project.rb

@@ -1293,6 +1293,22 @@ class Project < ActiveRecord::Base
     Gitlab::Redis.with { |redis| redis.del(pushes_since_gc_redis_key) }
   end
 
+  def environments_for(ref, commit, with_tags: false)
+    environment_ids = deployments.group(:environment_id).
+      select(:environment_id)
+
+    environment_ids =
+      if with_tags
+        environment_ids.where('ref=? OR tag IS TRUE', ref)
+      else
+        environment_ids.where(ref: ref)
+      end
+
+    Environment.where(id: environment_ids).map do |environment|
+      environment.includes_commit?(commit)
+    end
+  end
+
   private
 
   def pushes_since_gc_redis_key

app/views/projects/merge_requests/widget/_heading.html.haml

@@ -44,6 +44,7 @@
       Could not connect to the CI server. Please check your settings and try again.
 
 - @merge_request.environments.each do |environment|
+  - if can?(current_user, :read_environment, environment)
     .mr-widget-heading
       .ci_widget.ci-success
         = ci_icon_for_status("success")